There are actually a lot of studies that focus on emotional reactions and regulation for children who study. Some also use techniques like EEG and sensory data to measure how the body physically responds. That being said, it is very dangerous to claim a theory when there is no evidence. It is much better to share information when there is proof rather than fall back on the argument to makeup theories because there’s not a lot established yet. Just because there is little evidence doesn’t make that ideas or theories should be made up and pushed as foundational. That is how stereotypes and negative/false conclusions come into society and make it that much harder for people who stutter. This is also a theory that was proposed and since been disproven. Psychogenic stuttering is not comparable to developmental stuttering because they are different disorders and proceses in the brain. They don’t occur in the same way and cannot be compared to each other. Your statement about the brain failing to send signal doesn’t account for variation is also false. There are researchers that are currently investigating that (myself included) and there are theories being proposed based on various imaging data like EEG, fMRI and FNIRS imaging. The technology is still so new that people are still investigating but we are further than we were 10 years ago.